Regex validation for Email Address

Question

I need to validate whether my regex is correct for below scenario. Suggestion's if the regex is correct:

Wiki Link Local_part

The local-part of the email address may use any of these ASCII characters.[4] RFC 6531 permits Unicode characters beyond the ASCII range:

1. Uppercase and lowercase English letters (a–z, A–Z) (ASCII: 65–90, 97–122)
2. Digits 0 to 9 (ASCII: 48–57)
3. These special characters: ! # $ % & ' * + - / = ? ^ _ { | } ~ (limited support)
4. Character . (dot, period, full stop) (ASCII: 46) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively (e.g. [email protected] is not allowed).
5. Special characters are allowed with restrictions. They are:
6. Comments are allowed with parentheses at either end of the local part; e.g. "john.smith(comment)@example.com" and "(comment)[email protected]" are both equivalent to "[email protected]".
7. International characters above U+007F are permitted by RFC 6531, though mail systems may restrict which characters to use when assigning local parts.

The Regex:

^[a-z0-9][-a-z0-9.!#$%&'*+-=?^_`{|}~\/]+@([-a-z0-9]+\.)+[a-z]{2,5}$

Demo Here

Answer 1

I remember having read somewhere (possibly in another Code Review answer) that for an e-mail address, the simplest and most effective validation you can do is to make sure it contains an @. Making it more restrictive than that can often be a risk of invalidating some valid e-mails. You'd be surprised at some examples of valid e-mail addresses.

As an additional example, see the "almost RFC 822 compatible regex" in this answer.

Keep it simple, and don't mark some e-mail addresses that are actually valid as invalid.

email.contains("@")

If you want to be more restrictive than this, use an existing and trusted library for the validation, don't try to make another regex.

For further reading:

• http://en.wikipedia.org/wiki/Email_address#Validation_and_verification
• list of email addresses that can be used to test a javascript validation script on Stack Overflow
• http://codefool.tumblr.com/post/15288874550/list-of-valid-and-invalid-email-addresses

Answer 2

As @Simon pointed out, your regular expression might consider some valid addresses as invalid.

Per this source which I've found somewhere on this Stack Overflow page, this would be RFC5322-compliant:

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*
  |  "(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]
      |  \\[\x01-\x09\x0b\x0c\x0e-\x7f])*")
@ (?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?
  |  \[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}
       (?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:
          (?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]
          |  \\[\x01-\x09\x0b\x0c\x0e-\x7f])+)
     \])

Validating emails with a regular expression is ...more complicated than one would think, eh?

I agree with @Simon here, it's probably best to keep it simple, and go with a simple string.Contains() instead of a regular expression. If it's not a matter of life and death, ...don't try to be a regex ninja!

Answer 3

It was suggested that I move this to an answer instead of a comment:

Since you're using .NET, why not just use System.Net.Mail.MailAddress? It already performs validation in its constructor - it will throw a FormatException if the address is invalid.

This is particularly useful if you intend on using the address to actually send email, since you'll likely be using Systen.Net.Mail.MailAddress for it anyways.

This does not get you the regex, but I think a better solution is to avoid regex in this case for the reasons stated in the comments and other answers.

Answer 4

I follow the HTML5 spec for validation of email here. (Note that it's not RFC 5322 compatible)

The regex for it is:

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

which is simple enough for my needs.

Answer 5

If you're willing to take a dependency on System.ComponentModel.DataAnnotations then you can use the EmailAddressAttribute to do all the heavy lifting for you. I tend to use it as an extension method as follows:

private static readonly EmailAddressAttribute EmailValidator = new EmailAddressAttribute();

public static bool IsValidEmail(this string email)
{
    // You can also add validation against length if you want
    return !string.IsNullOrWhiteSpace(email) && EmailValidator.IsValid(email); 
}

Answer 6

Email validation regex:

^[a-z0-9][-a-z0-9._]+@([-a-z0-9]+\.)+[a-z]{2,5}$

Or

^[a-z0-9][-a-z0-9._]+@([-a-z0-9]+[.])+[a-z]{2,5}$

Test it out in this Demonstration

Answer 7

const re_host = '(([a-z0-9-]+\.)+[a-z]+|([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])){3})';
const re_localpart = '[a-z0-9!#\$%&\'*\+-/=\?\^_`{|}\~\.]+';

Take these two constants, and concatenate them like this re_localpart + '@' + re_host and you have a regular expression to validate an email address. Note that this is a PHP regex.